I see two problems with your site.
1. When I am getting e-mail that lists the articles, the font is so tiny on my 5.5" smartphone that it is impossible to read. The font cannot be adjusted. It is probably hard-coded.
2. Lately, the article (post) shown on mobile is wider than the screen while the font is bigger than usual. Again, the screen cannot be adjusted to accommodate entire width of the page.
Talk to your web designers - they are coding incorrectly and do not test enough after making changes.
I have Samsung Galaxy 8+ phone and have no problems with the o th her sites and mobile apps.
Customer support service by UserEcho